A simple business definition is to say that business occurs when someone does something for profit.
While we tend to think of profit in terms of money, it's actually a more encompassing term. In this business definition, profit includes symbols of money, such as credits, and items and services that are exchanged in lieu of money, such as barter.
A person who operates a business is described as self-employed, a business owner, a contractor, or sometimes as an entrepreneur. (The terms business owner and entrepreneur are not universally considered to be synonymous.)
People engaged in professions, trades and even "an undertaking of any kind" or "an adventure or concern in the nature of trade" can be considered to be in business, according to the Canada Revenue Agency. (See T4002 - Business and Professional Income.)
There are many different types of businesses, including service businesses, manufacturing businesses and retail businesses.
The legal structure of businesses varies from country to country. Forms of business ownership outlines the different forms of business available in Canada.
And in Canada, not all businesses need to be licensed and/or registered. Sole proprietorships that meet certain conditions, for example, don't need to be registered; see Do I Need to Register a Business Name? and Surprise! You're Running a Small Business.
If you are a non-Canadian interested in doing business in Canada, refer to this collection of articles on Doing Business in Canada for information on topics ranging from business immigration through how non-Canadians can open businesses in Canada.